1. Field of the Invention
The present invention relates to a method applied for an AC power source having a time-variant voltage level so as to stabilize work consumption of a passive element, and more particularly, to a method of stabilizing work consumption of a passive element by adjusting an input current provided to the passive element.
2. Description of the Prior Art
While an electronic product including passive elements is connected to a household AC power source, operations of the electronic product are easily affected by an unstable voltage level of the AC power source. While the electronic product includes light emitting diodes as its passive elements, since the light emitting diodes merely work under a condition that the voltage level of the AC power source is higher than a switch-on voltage of the light emitting diodes, stability of the light emitting diodes is significantly depending on stability of the AC power source.
Please refer to FIG. 1 and FIG. 2. FIG. 1 illustrates curve diagrams respectively indicating an input voltage/an input current/an input power of the light emitting diodes utilized by a conventional electronic product utilizing a household AC power source. FIG. 2 illustrates corresponding diagrams of FIG. 1 while the input voltage indicated at FIG. 1 varies.
As can be observed in an input voltage curve ac1 and an input current curve illustrated in FIG. 1, merely when the input voltage indicated by the input voltage curve ac1 is higher than a switch-on voltage VLED_ON of the light emitting diodes, the input current of the light emitting diodes is raised from zero to a constant current magnitude I_LED. Within the duration when the voltage level of the input voltage curve ac1 is higher than the switch-on voltage VLED_ON, i.e., the duration between the moments t1 and t2 shown in FIG. 1, consumption work of an input power source providing the input voltage equals to an area enveloped by an input power curve PC1 and a time difference between the moments t1 and t2, as shown by the italic line region in FIG. 1, where the input power curve PC1 is determined by the AC voltage ac1 and a line indicated the constant current magnitude I_LED. Note that a light-emitting output power P equals the switch-on voltage VLED_ON multiplied by the constant current I_LED. FIG. 2 illustrates a condition that the input voltage curve varies from ac1 to ac2 because of raise of an unstable input voltage of the light emitting diode, such as an AC voltage source. At this time, a duration, when the input voltage indicated by the input voltage curve ac2 is higher than the switch-on voltage VLED_ON, is lengthen from (t1−Δt) to (t2+Δt), where Δt indicates an negligible duration in comparison to (t2−t1). As can be observed from the area enveloped by the time difference (t2−t1) and the power curve PC1, and from the area enveloped by the time difference (t2+Δt)−t1−Δt) and the power curve PC2, the input work done by the input voltage source is increased and may be indicated by an enveloped area difference between enveloped area of the power curves PC1 and PC2, or may be indicated by a current-by-time raise equal to I_LED*2Δt; the enveloped area difference between the power curves PC1 and PC2 indicates an increased work because of the unstable input voltage, i.e., the area carrying upward arrows shown in FIG. 2. If the difference between the input voltage curves ac1 and ac2 is getting larger, the increased work from the input voltage source will render the luminance of the light emitting diode to be more unstable.